Pipe

ABSTRACT

A polyetheretherketone pipe of length greater than 250 meters and a residual stress of less than 5 MPa may be made using a calibrator device  2  which includes a cone shaped opening  6  arranged to receive a molten extruded pipe shaped polymer. Attached to the front member  4  is a vacuum plate  14   a  and successive vacuum plates  14   b - 14   h  are attached to one another to define an array of vacuum plates, the vacuum plates being arranged to allow a vacuum to be applied to a pipe precursor passing through opening  16 . The vacuum plates  14  also include temperature control means for heating or cooling the plates and therefore heating or cooling a pipe precursor passing through the openings. With a vacuum applied to opening  6, 16  and heating/cooling the plates, an extruded hot plastics pipe is inserted into calibrator  2  via opening  6  and conveyed through opening  16  in plates  14 , whereupon it is urged by the vacuum against the cylindrical surface defined by plates  14  to maintain its shape and the temperature of each plate is controlled to control the rate of cooling of the pipe precursor passing through. The pipe may be cooled at a relatively slow rate so that a pipe made from a relatively fast crystallising polymer crystalises and the crystallinity of the pipe along its extent and throughout its thickness is substantially constant.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/983,598 filed on Aug. 5, 2013, which is a national stage entry ofInternational Application No. PCT/GB2012/050267 filed on Feb. 7, 2012,which claims priority to United Kingdom Application No. 1102388.4 filedon Feb. 10, 2011.

BACKGROUND OF THE DISCLOSURE

This invention relates to a pipe and particularly, although notexclusively, relates to a pipe per se and methods of producing a pipe.Embodiments aim to extend the lifetime and/or reduce the risk ofpremature failure of a pipe which may carry a high pressure fluid (e.g.liquid (optionally containing particulates), gas or a mixture of thetwo) and/or be subjected to high external forces, in use. Preferredembodiments relate to pipes for use in the oil and/or gas industries forexample flexible risers arranged to transport fluids between floatingproduction units and a sub-sea wellhead. Other preferred embodiments maybe used in the aerospace industry, in process industries, in geometricaland mining industries and in industry in general.

It is well known to produce pipes by extruding molten polymers through asuitably shaped die and water quenching the extruded pipe, for exampleby directing it into a cool water bath and/or by spraying cool water onits outside. However, for fast crystallizing polymers and/or polymershaving a relatively high glass transition temperature such methods mayproduce pipes which have significant differences in crystallinity fromthe outside to the inside of the pipe wall. For example, the outsidewall of the pipe may have an amorphous (or very low crystallinity) skindue to rapid quenching of an extruded melt used in making the pipe,whereas on moving inwards, the crystallinity of the pipe wall mayincrease significantly. Such differences in crystallinity across thepipe wall lead to residual hoop stress. For example, in a 4.2 inch (10.6cm) outside diameter (OD) pipe, the residual hoop stress (calculated asdescribed hereinafter) may be in excess of 5.6 MPa. In general, residualstress may be caused by molecular orientation frozen in during themanufacturing process or thermal stresses due to different coolingrates. Such residual stress is a consequence of the thermal contractionof the melt being restricted during non-uniform solidification whichfreezes in a strain. Such high residual stress can lead to problems. Forexample, if such pipes are sawn, the pipe may shatter as the stressesare released. Alternatively, and/or additionally, the pipes may be moresusceptible to failure through fatigue and/or stress in use. A highlystressed pipe is more likely to fail (e.g. crack catastrophically) in ashorter time in use than a pipe with lower residual stress.

It is desirable to maximise the useful lifetimes of pipes and/or reducethe risk of premature failure. It is an object of the present inventionto address this problem.

BRIEF SUMMARY OF THE DISCLOSURE

According to a first aspect of the invention, there is provided a pipehaving a length of at least 1 m and a residual stress of less than 5MPa, wherein said pipe comprises:

(i) a polymeric material which includes:

-   -   (a) phenyl moieties;    -   (b) ether and/or thioether moieties; and, optionally,    -   (c) ketone and/or sulphone moieties; and/or        (ii) a polymeric material with a crystallinity half-life        (t_(0.5)) at 15° C. above its glass transition temperature (Tg)        of less than 1000 seconds.

The residual stress may be measured by at least one of the methods inExample 1 hereinafter.

In the context of the present specification, the reference to a “pipe”includes articles that may alternatively be referred to as “tubes”.

Said length of said pipe suitably refers to a continuous uninterruptedlength of pipe. The length of pipe suitably does not comprise individualpipe sections which are joined to one another. Suitably the entirelength of pipe is extrudable and/or extruded in a single extrusionprocess. The pipe suitably has a substantially constant cross-sectionalong its entire extent. Said pipe preferably has a circularcross-section. Said pipe is suitably annular. Said pipe preferably hassubstantially smooth outer surface suitably across substantially itsentire extent.

Said pipe may have a length of at least 2 m, at least 5 m, at least 8 mat least 10 m, suitably at least 15 m, preferably at least 50 m, morepreferably at least 100 m, especially at least 250 m. In some cases thelength may be greater than 1000 m.

In one embodiment, pipe is continuously extruded and, suitably,properties of the pipe, for example residual stress as described, arethe same magnitude when assessed at a first end of the pipe, at a secondend of the pipe opposite to that of the first end and in the middle ofthe pipe, exactly between said first and second ends. Such extruded pipemay be cut into a multiplicity, for example 0.5 m, 1 m or 2 m, lengths.Advantageously, the properties of the cut pipes of the same length (andsuitably pipes of different lengths) are substantially the same as oneanother.

Said pipe may have an outside diameter of at least 0.6 cm, suitably atleast 2.5 cm, preferably at least 7 cm, more preferably at least 10 cm,especially at least 15 cm. The diameter may be less than 50 cm,preferably less than 40 cm, more preferably less than 30 cm. In someembodiments (e.g. aerospace) the outside diameter may be in the range 12mm to 50 mm.

The outer diameter of the pipe may be defined as “d” cm and thethickness of the pipe wall may be defined as “t” cm. The SDR of the pipe(defined as the diameter (d) to thickness (t) ratio) may be at least 6and is suitably in the range 15 to 40.

The thickness of the wall which defines the pipe may be at least 0.5 mm,suitably is at least 0.8 mm, and preferably is 1 mm or more. Thethickness may be less than 30 mm, suitably less than 15 mm, preferablyless than 10 mm, more preferably less than 8 mm, especially less than 6mm. The thickness is preferably in the range 0.6 mm to 6 mm.

Said pipe may have a residual stress of less than 4 MPa, suitably lessthan 3 MPa, preferably less than 2.5 MPa, especially 2 MPa or less.

It is preferred for the crystallinity across the cross-section of thepipe not to vary too much, thereby to minimise residual hoop stress.FTIR may be used to assess crystallinity and this may be used to assessthe level of crystallinity at a surface and/or across the thickness of asample. Reference is made to a paper titled “Crystallinity inPoly(Aryl-Ether-Ketone) Plaques Studied by Multiple Internal ReflectionSpectroscopy” (Polymer Bull, 11, 433 (1984)). The difference incrystallinity between an outer surface of the pipe and an inner surfaceof the pipe, measured by FTIR as described, may be less than 10%,suitably less than 8%, preferably less than 6%, especially less than 4%.Suitably, the difference between the highest crystallinity at anyposition on the pipe and the lowest crystallinity at any position on thepipe is less than 10%, suitably less than 8%, preferably less than 6%,especially 4% or less.

Said polymeric material is suitably semi-crystalline and may be suchthat the kinetics of crystallisation are so fast that it issubstantially impossible to produce a solid from the polymeric materialwhich is fully amorphous. For example, the crystallinity half-life(t_(0.5)) of the polymeric material at 15° C. above its Tg may be lessthan 1000 seconds, less than 500 seconds, less than 250 seconds, or lessthan 150 seconds determined in accordance with the description in J.Brandrup, E. H. Immergut and E. A. Grulke, Polymer Handbook 4^(th)Edition, Wiley Interscience, 1999, ISBN 0-471-47936-5 (Vol 1) and0-471-48172-6 (Vol 2).

On the aforementioned basis the t_(0.5) for polyetheretherketone at 160°C. (which is close to 15° C. above its Tg) is 126 seconds whichindicates that crystallisation occurs very rapidly.

Said pipe preferably comprises, more preferably consists essentially of,a single said polymeric material or a single homogenous polymericcomposition comprising said polymeric material. Thus, said pipe ispreferably substantially homogenous, although it may comprise a polymerhaving different levels of crystallinity (as described above) between aninside and outside surface of the pipe. Said pipe preferably consistsessentially of a single said polymeric material.

Said polymeric material suitably has a Tg of greater than 50° C.,preferably greater than 75° C., more preferably greater than 85° C. orgreater than 100° C. Said polymeric material may have a Tg of less than260° C., for example less than 220° C. or less than 200° C. In somecases, the Tg may be less than 190° C., 180° C. or 170° C. Said,polymeric material preferably has a Tg of greater than 50° C., morepreferably greater than 80° C., especially greater than 120° C.

Said polymeric material suitably has a melt viscosity (MV) of at least0.06 kNsm⁻², preferably has a MV of at least 0.08 kNsm⁻², morepreferably at least 0.085 kNsm⁻², especially at least 0.09 kNsm⁻². MV issuitably measured using capillary rheometry operating at 400° C. at ashear rate of 1000 s⁻¹ using a tungsten carbide die, 0.5×3.175 mm. Saidpolymeric material may have a MV of less than 1.00 kNsm⁻², suitably lessthan 0.8 kNsm⁻².

Said polymeric material may have a tensile strength, measured inaccordance with ASTM D790 of at least 40 MPa, preferably at least 60MPa, more preferably at least 80 MPa. The tensile strength is preferablyin the range 80-110 MPa.

Said polymeric material may have a flexural strength, measured inaccordance with ASTM D790 of at least 145 MPa. The flexural strength ispreferably in the range 145-180 MPa, more preferably in the range145-165 MPa.

Said polymeric material may have a flexural modulus, measured inaccordance with ASTM D790, of at least 2 GPa, preferably at least 3 GPa,more preferably at least 3.5 GPa. The flexural modulus is preferably inthe range 3.5-4.5 GPa, more preferably in the range 3.5-4.1 GPa.

Preferably, said polymeric material has a moiety of formula

and/or a moiety of formula

and/or a moiety of formula

wherein m, r, s, t, v, w and z independently represent zero or apositive integer, E and E′ independently represent an oxygen or asulphur atom or a direct link, G represents an oxygen or sulphur atom, adirect link or a —O-Ph-O— moiety where Ph represents a phenyl group andAr is selected from one of the following moieties (i)**, (i) to (iv)which is bonded via one or more of its phenyl moieties to adjacentmoieties

Unless otherwise stated in this specification, a phenyl moiety has 1,4-,linkages to moieties to which it is bonded.

In (i), the middle phenyl may be 1,4- or 1,3-substituted. It ispreferably 1,4-substituted.

In one embodiment, a polymeric material may comprise a repeat unit offormula I and no other repeat units. Said polymeric material may bepolyphenylenesulphide (PPS).

In a preferred embodiment, said polymeric material may include more thanone different type of repeat unit of formula I; and more than onedifferent type of repeat unit of formula II; and more than one differenttype of repeat unit of formula III. Preferably, however, only one typeof repeat unit of formula I, II and/or III is provided.

Said moieties I, II and III are suitably repeat units. In the polymericmaterial, units I, II and/or III are suitably bonded to one another—thatis, with no other atoms or groups being bonded between units I, II andIII.

Phenyl moieties in units I, II and III are preferably not substituted.Said phenyl moieties are preferably not cross-linked.

Where w and/or z is/are greater than zero, the respective phenylenemoieties may independently have 1,4- or 1,3-linkages to the othermoieties in the repeat units of formulae II and/or III. Preferably, saidphenylene moieties have 1,4-linkages.

Preferably, the polymeric chain of the polymeric material does notinclude a —S— moiety. Preferably, G represents a direct link.

Suitably, “a” represents the mole % of units of formula I in saidpolymeric material, suitably wherein each unit I is the same; “b”represents the mole % of units of formula II in said polymeric material,suitably wherein each unit II is the same; and “c” represents the mole %of units of formula III in said polymeric material, suitably whereineach unit III is the same. Preferably, a is in the range 45-100, morepreferably in the range 45-55, especially in the range 48-52.Preferably, the sum of b and c is in the range 0-55, more preferably inthe range 45-55, especially in the range 48-52. Preferably, the ratio ofa to the sum of b and c is in the range 0.9 to 1.1 and, more preferably,is about 1. Suitably, the sum of a, b and c is at least 90, preferablyat least 95, more preferably at least 99, especially about 100. Suitablyb is at least 20, preferably at least 40, more preferably at least 45.Preferably, a is 20 or less, preferably 10 or less, more preferably 5 orless. Preferably, said polymeric material consists essentially ofmoieties I, II and/or III.

Said polymeric material may be a homopolymer having a repeat unit ofgeneral formula

or a homopolymer having a repeat unit of general formula

or a random or block copolymer of at least two different units of IVand/or Vwherein A, B, C and D independently represent 0 or 1 and E, E′, G, Ar,m, r, s, t, v, w and z are as described in any statement herein.

Suitably in IV, at least one of A and B represents 1. Suitably in V atleast one of C and D represents 1.

Preferably, m is in the range 0-3, more preferably 0-2, especially 0-1.Preferably, r is in the range 0-3, more preferably 0-2, especially 0-1.Preferably t is in the range 0-3, more preferably 0-2, especially 0-1.Preferably, s is 0 or 1. Preferably v is 0 or 1. Preferably, w is 0or 1. Preferably z is 0 or 1.

Preferably, said polymeric material is a homopolymer having a repeatunit of general formula IV.

Preferably Ar is selected from the following moieties (xi)** and (vii)to (x)

In (vii), the middle phenyl may be 1,4- or 1,3-substituted. It ispreferably 1,4-substituted.

Suitable moieties Ar are moieties (i), (ii), (iii) and (iv) and, ofthese, moieties (i), (ii) and (iv) are preferred. Other preferredmoieties Ar are moieties (vii), (viii), (ix) and (x) and, of these,moieties (vii), (viii) and (x) are especially preferred.

Said polymeric material suitably includes at least 60 mole %, preferablyat least 70 mole %, more preferably at least 80 mole %, especially atleast 90 mole % of repeat units which do not include —S— or —SO₂—moieties. Said polymeric material suitably includes at least 60 mole %,preferably at least 70 mole %, more preferably at least 80 mole %,especially at least 90 mole % of repeat units which consist essentiallyof phenyl moieties, ether moieties and ketone moieties.

An especially preferred class of polymeric materials are polymers (orcopolymers) which consist essentially of phenyl moieties in conjunctionwith ketone and/or ether moieties. That is, in the preferred class, thepolymeric material does not include repeat units which include —S—,—SO₂— or aromatic groups other than phenyl. Preferred polymericmaterials of the type described include:

-   -   (a) a polymer consisting essentially of units of formula IV        wherein Ar represents moiety (iv), E and E′ represent oxygen        atoms, m represents 0, w represents 1, G represents a direct        link, s represents 0, and A and B represent 1 (i.e.        polyetheretherketone).    -   (b) a polymer consisting essentially of units of formula IV        wherein E represents an oxygen atom, E′ represents a direct        link, Ar represents a moiety of structure (i), m represents 0, A        represents 1, B represents 0 (i.e. polyetherketone);    -   (c) a polymer consisting essentially of units of formula IV        wherein E represents an oxygen atom, Ar represents moiety (i), m        represents 0, E′ represents a direct link, A represents 1, B        represents 0, (i.e. polyetherketoneketone).    -   (d) a polymer consisting essentially of units of formula IV        wherein Ar represents moiety (i), E and E′ represent oxygen        atoms, G represents a direct link, m represents 0, w represents        1, r represents 0, s represents 1 and A and B represent 1. (i.e.        polyetherketoneetherketoneketone).    -   (e) a polymer consisting essentially of units of formula IV,        wherein Ar represents moiety (iv), E and E′ represents oxygen        atoms, G represents a direct link, m represents 0, w represents        0, s, r, A and B represent 1 (i.e. polyetheretherketoneketone).    -   (f) a polymer comprising units of formula IV, wherein Ar        represents moiety (iv), E and E′ represent oxygen atoms, m        represents 1, w represents 1, A represents 1, B represents 1, r        and s represent 0 and G represents a direct link (i.e.        polyether-diphenyl-ether-phenyl-ketone-phenyl-).

The main peak of the melting endotherm (Tm) for said polymeric materialmay be at least 300° C.

Said polymeric material may consist essentially of one of units (a) to(f) defined above.

Said polymeric material preferably comprises, more preferably consistsessentially of, a repeat unit of formula (XX)

where t1, and w1 independently represent 0 or 1 and v1 represents 0, 1or 2. Preferred polymeric materials have a said repeat unit whereint1=1, v1=0 and w1=0; t1=0, v1=0 and w1=0; t1=0, w1=1, v1=2; or t1=0,v1=1 and w1=0. More preferred have t1=1, v1=0 and w1=0; or t1=0, v1=0and w1=0. The most preferred has t1=1, v1=0 and w1=0.

In preferred embodiments, said polymeric material is selected frompolyetheretherketone, polyetherketone, polyetherketoneetherketoneketoneand polyetherketoneketone. In a more preferred embodiment, saidpolymeric material is selected from polyetherketone andpolyetheretherketone. In an especially preferred embodiment, saidpolymeric material is polyetheretherketone.

Said pipe may comprise or consist essentially of a polymeric compositionwhich includes said polymeric material and one or more fillers.

Said polymeric material may make up at least 60 wt %, suitably at least70 wt %, preferably at least 80 wt %, more preferably at least 90 wt %,especially at least 95 wt %, of the total amount of thermoplasticpolymeric materials in said polymeric composition from which said pipeis made.

A single said polymeric material is preferably substantially the onlythermoplastic polymer in said polymeric composition. Suitably, areference to a thermoplastic polymer refers to a polymer which is meltedin the formation of said pipe.

A filler is suitably a material which is not melted in manufacture ofsaid pipe. It suitably has a melting temperature of greater than 350° C.

Said filler may include a fibrous filler or a non-fibrous filler. Saidfiller may include both a fibrous filler and a non-fibrous filler. Asaid fibrous filler may be continuous or discontinuous. A said fibrousfiller may be selected from inorganic fibrous materials, non-melting andhigh-melting organic fibrous materials, such as aramid fibres, andcarbon fibre. A said fibrous filler may be selected from glass fiber,carbon fibre, asbestos fiber, silica fiber, alumina fiber, zirconiafiber, boron nitride fiber, silicon nitride fiber, boron fiber,fluorocarbon resin fibre and potassium titanate fiber. Preferred fibrousfillers are glass fibre and carbon fibre. A fibrous filler may comprisenanofibres.

A said non-fibrous filler may be selected from mica, silica, talc,alumina, kaolin, calcium sulfate, calcium carbonate, titanium oxide,ferrite, clay, glass powder, zinc oxide, nickel carbonate, iron oxide,quartz powder, magnesium carbonate, fluorocarbon resin, graphite,polybenzimidazole (PBI), carbon powder, nanotubes and barium sulfate.The non-fibrous fillers may be introduced in the form of powder or flakyparticles.

Preferably, said filler comprises one or more fillers selected fromglass fibre, carbon fibre, carbon black and a fluorocarbon resin. Morepreferably, said filler comprises glass fibre or carbon, especiallydiscontinuous, for example chopped, glass fibre or carbon fibre.

Said polymeric composition suitably includes 35-100 wt %, preferably50-100 wt %, more preferably 65-100 wt % of said polymeric material.

Said polymeric composition suitably does not include a reinforcingfiller (e.g. carbon fibre) but may include a non-reinforcing filler(e.g. talc or carbon black) which may be included to reduce costs and/orto colour the pipe. However, such a filler could detrimentally increasethe roughness of the inside of the pipe and therefore increase pipelosses in the fluid flowing through it. To address this, the inside ofthe pipe could be provided (e.g. by coextrusion) with a layer comprisingsubstantially 100 wt % of unfilled polymeric material (e.g. the samepolymeric material as in said polymeric composition).

Suitably, the total amount of filler in said polymeric composition is 65wt % or less, or 60 wt % or less. Said polymeric composition may include0-65 wt %, preferably 0-50 wt %, more preferably 0-35 wt % of filler.Preferably, said polymeric composition includes less than 5 wt % and,more preferably, includes substantially no filler means.

Preferably, said pipe consists essentially of a polymeric material offormula (XX) and, especially, consists essentially ofpolyetheretherketone.

Said pipe may be part of an assembly. Said assembly may comprise saidpipe as an inner part which is surrounded by an outer part. Said outerpart is preferably arranged around substantially the entirety of thecircumferential outer wall of said pipe. Said outer part may be arrangedto reinforce the pipe; it is suitably arranged to resist mechanicaland/or thermal loads to which said assembly may be exposed in use. Forexample, said outer part may be arranged to restrict compression of saidpipe due to the weight of water that may act on it in use and/or torestrict expansion of said pipe due to flow of a hot pressure fluidtherethrough in use. Said outer part of said assembly may comprise afirst material and a second material. Said first material may comprise athermoplastic or thermosetting resin. Said resin may be of any suitabletype, for example a polyamide, polysulphone, polyetherimide,polyethersulphone or any of the polymeric materials comprising (a)phenyl moieties; (b) ketone and/or sulphone moieties; an/or (c) etherand/or thioether moieties described above for said pipe. Preferably,said first material is selected from homopolymers or copolymerscomprising units IV and/or V referred to above. More preferably, saidfirst material is of general formula (XX) as described above.

Said second material may comprise a fibrous material. Said fibrousmaterial may independently have any feature of the fibrous fillerdescribed above in the context of filler optionally included in saidpipe. Said fibrous material may be continuous or discontinuous. It ispreferably selected from glass, aramid or carbon fibres.

Said outer part may include 25-75 wt % (more preferably 35-75 wt %) ofsaid first material and 25-75 wt % (more preferably 25-65 wt %) of saidsecond material. Said outer part may comprise a substantially homogenousarrangement of said first and second materials.

The outer part is preferably flexible and arranged to be wrapped aroundsaid pipe. It may be elongate and it may comprise a tape, mat or wovenstructure.

Said outer part may define a reinforcing layer around said pipe of athickness of at least 0.25 mm, at least 0.5 mm or at least 1 mm. Thethickness may be in the range 1 mm to 80 mm, for example 1 mm to 50 mm.The outer part may itself comprise many layers (e.g. greater than 10,25, 40, 70 or 90 layers) of, for example tape, overlaying one another.

According to a second aspect of the invention, there is provided amethod of making a pipe, for example a pipe of the first aspect, themethod comprising:

(i) selecting a calibrator device which includes an elongate opening forreceiving a hot extruded pipe, wherein said opening includes a vacuumapplying region arranged to apply a vacuum to a pipe within the opening,said device further including at least two cooling regions which arespaced apart along its extent, said cooling regions being arranged tocool a pipe within the opening;(ii) selecting the respective level of vacuum to be applied to saidvacuum applying region;(iii) selecting the respective level of cooling to be applied by saidcooling regions;(iv) introducing a hot extruded pipe into said elongate opening in saidcalibrator and conveying said pipe through said elongate opening;(v) applying a vacuum to said pipe in said vacuum applying region; andcooling said pipe in said cooling regions as the pipe is conveyed alongsaid elongate opening.

Said elongate opening suitably includes a mouth at an end for receivingthe extruded pipe, wherein said mouth includes an outer surface which iscooled in order to solidify said hot pipe (e.g. the outer surface onlyof the pipe), on contact therewith and facilitate its passage intoand/or through the elongate opening. Said mouth is suitably taperedinwardly (on moving in the direction of insertion of the pipethereinto). The outer surface of the mouth (which suitably contacts thepipe in use) is suitably cooled. It is suitably cooled to a temperaturewhich is lower than the temperature of a surface of the elongate openingwhich contacts said pipe which is immediately downstream of said mouth.

The method may include manufacturing the pipe in an extruder anddirecting hot (e.g. molten) pipe from said extruder into said calibratorto control the crystallinity of the pipe as described.

The method may include independently controlling at least two of saidcooling regions so that the surfaces of the two regions which contactthe pipe in use are arranged to cool the pipe at different rates and/orsaid surfaces may be cooled to different temperatures.

The method of the second aspect may be for making a pipe of the firstaspect.

According to a third aspect of the invention, there is provided acalibrator device for manufacturing a pipe, said calibrator deviceincluding an elongate opening for receiving a hot extruded pipe, whereinsaid opening includes a vacuum applying region arranged to apply avacuum to a pipe within the opening, said device further including atleast two cooling regions which are spaced apart along its extent, saidcooling regions being arranged to cool a pipe within the opening.

Said device may be for carrying out the method of the second aspect.

Said device may be for producing a pipe according to the first aspect.

As described according to the first aspect, a continuous length of pipemay be extruded and this may be cut into individual lengths, for exampleof at least 0.4 m, at least 0.6 m, at least 1 m or at least 2 m. Theindividual lengths may be less than 10 m or less than 5 m.Advantageously, the cut lengths are substantially the same as oneanother, for example in terms of residual stress (suitably as describedaccording to the first aspect) and/or crystallinity. Thus, in a fourthaspect, there is provided a collection of lengths of pipe (preferablycomprising at least 5 lengths of pipe of the same dimensions) having aresidual stress as described accordingly to the first aspect and/or havea difference in crystallinity as described according to the first aspect

The collection of lengths may be juxtaposed but not connected to oneanother; or the lengths may be connected to define a combined length ofsaid pipes.

DESCRIPTION OF THE DRAWINGS

Specific embodiments of the invention will now be described, by way ofexample, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a calibrator for use in production ofpipes;

FIG. 2 is a front view in the direction of arrow II of FIG. 1, in moredetail;

FIG. 3 is a cross-section along line III-III of FIG. 2;

FIG. 4 is a cross-section through one vacuum plate;

FIG. 5 is a perspective view of the vacuum plate; and

FIG. 6 is a perspective view in the direction of arrow VI of FIG. 3.

FIGS. 7a and 7b are plan views of rings made from pipes manufacturedaccording to the prior art and invention respectively.

DETAILED DESCRIPTION OF THE DISCLOSURE

In the figures, the same or similar parts are annotated with the samereference numerals.

The following material is referred to hereinafter

VICTREX PEEK refers to polyetheretherketone grade 450G obtained fromVictrex, Thornton Cleveleys, UK.

In the figures, the same or similar parts are annotated with the samereference numerals.

Referring to FIG. 1, the calibrator 2 comprises a front member 4 whichincludes a centrally positioned inwardly tapering cone-shaped opening 6arranged to receive molten extruded pipe-shaped polymer. The front plateincludes internal channels (not shown in FIG. 1) for receiving coolantfor cooling the molten polymer. An opening communicates with theinternal channels and defines an inlet 8 for coolant and an outlet 10communicates with the channels and provides an outlet for coolant. Inaddition, front member 4 incorporates openings (not shown in FIG. 1)which extend from the outside and open into cone-shaped opening 6, sothat a passageway extends from outside the front member to opening 6 viawhich passageway a vacuum may be applied to the outside of a pipeprecursor present within opening 6.

Attached to the front member 4 is a vacuum plate 14 a and successivevacuum plates 14 b-14 h are attached to one another to define an arrayof vacuum plates. Each vacuum plate includes a circular opening 16arranged such that the openings together define a circular cross-sectionopening which is axially aligned with cone-shaped opening 6 so that anextruded pipe precursor formed can pass through openings 6, 16.

The vacuum plates 14 also incorporate openings (not shown in FIG. 1)which extend from outer cylindrical walls 18 thereof and open intocircular opening 16 so that a passageway extends from outside eachvacuum plate 14 to the circular opening 16 defined therein. Thepassageway enables a vacuum to be applied to a pipe precursor passingthrough openings 16.

The vacuum plates 14 also include temperature control means for heatingor cooling the plates and therefore heating or cooling a pipe precursorpassing through the openings 16. In one embodiment, vacuum plate 14 amay include a fluid inlet 20 for a heating or cooling fluid and plates14 a to 14 h are arranged for passage of heating/cooling fluid frominlet 20 via passageways defined in each plate 14 a to 14 h and out ofoutlet 22 in plate 14 h. In another embodiment, each vacuum plate mayinclude a respective inlet and outlet, such that each respective vacuumplate 14 is served by its own heating/cooling fluid and each vacuumplate 14 can therefore be individually cooled or heated to apredetermined temperature as may be required. In the latter embodiment,adjacent plates may be thermally insulated from one another tofacilitate individual temperature control.

The array of vacuum plates 14 is arranged within an hermetically sealedhousing 23 in which a vacuum can be produced by suitable means (notshown). The vacuum is communicated via the passageways which extend fromoutside each vacuum plate 14 to the circular openings 16 so that thevacuum can be applied to a pipe precursor passing through openings 16.

In general terms, the FIG. 1 apparatus may be operated as follows.

Initially, a vacuum is applied to openings 6, 16 and heating/coolingfluid is passed through plates 14 via the inlet 20 and outlet 22 (or viarespective inlets/outlets associated with each plate); andheating/cooling fluid is passed through inlet 8 and outlet 10 of frontmember 4. Also, coolant is passed through front plate 4 via openings 8,10.

An extruded hot plastics pipe precursor of appropriate diameter andthickness defined by a pipe die fixed to the extruder is then insertedinto calibrator 2 via opening 6. The temperature of member 4 is such asto freeze the outside wall of the pipe precursor and stop it sticking tomember. Thereafter, the pipe precursor is conveyed through openings 16in plates 14. During passage of the pipe precursor 16, it is urged bythe vacuum against the cylindrical surface defined by plates 14 tomaintain its shape and the temperatures of each plate is controlled tocontrol the rate of cooling of the pipe precursor passing through. Theformed pipe exits the calibrator 2 as represented by arrow 24, afterwhich it may be allowed to cool to ambient temperature.

The heating/cooling of plates 14 may be adjusted to cool the pipeprecursor at a relatively constant rate. A relatively slow rate may beselected so that a pipe made from a relatively fast crystallizingpolymer (like polyetheretherketone) crystallises so that thecrystallinity of the pipe along its extent and throughout its thicknessis substantially constant. A pipe may therefore be made which has low ornegligible residual stress.

As an alternative, the calibrator may be used to deliberately form apipe having different levels of crystallinity across its thickness. Forexample, a pipe may be made having a skin which is relatively amorphouswith the wall of the pipe inwards of the skin having relatively highcrystallinity.

FIGS. 2 to 5 show parts of the calibrator of FIG. 1 in more detail.

The front member 4 includes a square cross-section plate 30 which isarranged to define one wall of housing 23. Opening 8 for receivingcoolant communicates with an annular opening 32 defined within a body 34which also defines the opening 6 for passage of the pipe precursor. Thecoolant is arranged to circulate within the body 34 in order to cool thesurface of opening 6. Outlet 10 also communicates with opening 32 forremoving coolant from the body. Body 34 is suitably made from athermally conductive material, for example brass.

The body 34 also defines a series of annular recesses 36 having mouthswhich open into opening 6 and which communicate with axial ports 38.Axial ports 38 are connected to passageways which extend to a positionoutside body 34 (in substantially the same manner as described withreference to FIG. 5 hereinafter) so that a vacuum can be applied toopening 6 by removal of gas from opening 6 via recesses 36 and axialports 38.

In FIG. 3, vacuum plates 14 a-j are shown which are identical. More orfewer such plates may be provided as required for any particularsituation.

Each vacuum plate 14 may be as shown in FIGS. 4 and 5. The plate 14includes ports 40, via which one plate may be secured to another. At oneside 44, four radially-extending cut-outs 46 (FIG. 5) are defined whichcommunicate with an annular cut-out 48 which includes eightaxially-extending elongate openings 50 defined within it. The openings50 communicate with an annular slot 52 defined in wall 54 which definescircular opening 16. Thus, an airflow passageway is defined whichextends from opening 6, via slot 52, axially-extending openings 50 andcut-outs 46 to a position outside the plate 14 by means of which thevacuum can be applied to a pipe precursor arranged within opening 6.

Plate 14 also includes an annular opening 60 defined within body 62which communicates with radially-extending ports in the body (e.g. port64 in FIG. 5 and a diametrically opposing port not shown) forcirculating coolant/heating fluid within the body 62 to cool/heat it. Itwill be appreciated that each plate 14 may have its own supply ofcoolant/heating fluid so that the temperature of each plate 14 may beindividually controlled. By selection of appropriate dimensions for theradially-extending ports and the output of the pump used to circulatethe fluid, the fluid may be caused to flow turbulently within the body.Plate 14 is suitably arranged so that the temperature of wall 54 issubstantially the same across its surface area.

The plates 14 are suitably arranged (e.g. by use of coolant/heatingfluids of appropriate temperature) in such a way as to avoidlarge/abrupt temperature changes across a surface of wall 54 of anindividual plate 14 and between adjacent plates 14. In use, to this end,adjacent plates 14 may be arranged with the ports via which fluid isdelivered to opening 6 (e.g. port 64 in FIG. 5) and removed therefrombeing staggered relative to one another and/or the inlet for fluid for afirst plate 14 may be on a first side of the calibrator and the outletmay be on an opposite side, whereas the second plate 14 adjacent thefirst plate 14 may have its inlet for fluid on the second side and itsoutlet on the first side. Alternatively, inlets of adjacent plates 14may be staggered at 45° to one another; and outlets may be arrangedsimilarly.

Thus, by providing a series of separate plates 14, the temperature ofspecific regions along the calibrator may be individually controlled.More or fewer plates 14 may be included to adjust the length of thecalibrator, to allow it to be used to process pipes at differentspeeds—e.g. a longer calibrator may be used to process pipes at lowerspeeds. In addition, in some embodiments, it may be desirable to use avariable vacuum (e.g. vary the level of vacuum between groups ofplates), to facilitate production of a circular cross-section pipe.

The calibrator may be of utility in the manufacture of pipes from arange of polymeric materials. It may be particularly advantageous in themanufacture of pipes from crystallisable polymeric materials havingrelatively high glass transition temperatures (because for such high Tgpolymers, conventional water quenching ensures a too high rate oftemperature drop to below Tg which generates additional stress) and/orpolymeric materials which are relatively fast crystallizing. In thelatter case, if such a polymeric material is cooled too quickly it willcrystallise to different extents from one side of the pipe to anopposite side leading to different levels of crystallinity across thepipe, which may lead to problems as herein before described.

Examples of polymeric materials which may advantageously be used in themanufacture of pipes using the calibrator include polyaryletherketones,for example polyetheretherketone (PEEK) and polyphenylene sulphide(PPS).

The calibrator 2 has great versatility for controlling and/or definingcrystallinity in a desired manner for pipes of a range of cross-sectionsand wall thicknesses. Steps in manufacturing a pipe in a desired forminclude the following:

(i) Selecting the pipe diameter and wall thickness. For example, forvery thin wall pipes (e.g. of 0.5 mm minimum wall thickness), it isdifficult to avoid producing a relatively low crystallinity (oftenreferred to as “amorphous”) skin due to rapid cooling of the outer wallof the pipe. Thus, the wall thickness will have a bearing on othervariables associated with the calibrator. Similarly, the pipe diameterwill have implications for the design of the calibrator and ensuringdesired cooling rates are achieved.(ii) Selecting the calibrator. Although FIG. 3 shows a calibrator havingten vacuum plates 14, fewer or more plates may be included, for example,if it is desired to increase the speed of passage of a pipe through thecalibrator, but maintain the cooling rate, then the calibrator may beextended. A doubling of the speed of passage may necessitate a doublingof the number of plates 14. Similarly, shorter calibrators may be usedfor lower speed throughput.(iii) Selecting the temperature of each plate 14 and adjusting thetemperatures and/or identity of heating/cooling fluid used. For example,when the FIG. 3 calibrator is used to make a PEEK pipe, the first member4 may be cooled to maintain it in use at a temperature of 80° C. orbelow to freeze the outside of the molten PEEK pipe precursor on entryinto the calibrator and stop it sticking within opening 6. In addition,the plates 14 a and 14 b may be cooled (typically to within the range100° C. to 200° C., although some plates could be cooled to as low as 5°C.) to provide a gradual temperature transition to plate 14 c andsubsequent plates. It should also be borne in mind that for PEEK, theheat of crystallisation is emitted in the range 212-215° C. and thepotential increase in energy will need to be offset by a lowertemperature for the relevant plate 14, in order to provide gradualtemperature changes and balanced thermodynamics along the calibrator. Ina typical example, all of the plates may be substantially the sametemperature (e.g. about 70 to 120°).

Typically, water may be used to cool first member 4; and oil may be usedto cool the other plates. 0:1 cooling may be used in some circumstances.

After selecting and setting up the calibrator, taking relevant variablesinto consideration, a pipe having a desired level and/or arrangement ofcrystallinity may be manufactured.

Initially, the calibrator 2 is readied by operating a vacuum device toextract air from within housing 23 and thereby apply a vacuum, asdescribed, around opening 6 through which a pipe precursor is to pass.Also, heating/cooling fluid as applicable is passed through front member4 and vacuum plates 14 so they reach equilibrium at a desiredtemperature. PEEK is then extruded using suitable apparatus to produce amolten pipe precursor which is introduced into cone-shaped opening 6. Amelt skin is formed on the molten pipe by contact of the melt with frontplate 4 which is cooled as described. The front plate defines a taperangle of about 45° which is found to be optimum for capturing the moltenpipe and cooling it. (The taper angle is the angle defined between anelongate axis of the front plate and the cone-shaped wall of the frontplate). If there is insufficient cooling, the melt is too weak; and ifthe cooling is too great the melt sticks to the plate and the extrudatepiles up on plate 4 and does not progress along the calibrator.

Typically, the speed of introduction and/or passage of the pipeprecursor into and through the calibrator may be at a constant rate,suitably in the range 0.1 m/min to 10 m/min.

As the pipe precursor enters opening 6, its outer surface solidifies toprevent it sticking within the opening as described above. Then the pipeprecursor passes through successive plates 14, wherein it is graduallyand controllably cooled, for example to maximise its crystallinity andmaximize the homogeneity of its crystallinity—i.e. so that thecrystallinity across the thickness of the pipe wall is substantiallyconstant.

On passage from the calibrator, the pipe may be at an elevatedtemperature and may be wound around a reel and allowed to cool toambient temperature; or it may be cooled, for example using water,before being wound round a reel. In an alternative embodiment, the pipepassing out of the calibrator may be cut to specific lengths. Once thecalibrator has been set up, it may be used to manufacture a very longlength of pipe (e.g. as much at 3000-4000 m) having consistentproperties, for example crystallinity along its extent; or it may beused to manufacture shorter lengths of pipe which have consistentproperties. The calibrator may be particularly suitable formanufacturing pipes having an SDR (Standard Dimension Ratio) (diameterof pipe to thickness of pipe wall ratio) of greater than 6. Theadvantageous nature of pipes made as described may be illustrated bymeasuring the residual stress in the pipe. This may be measured asdescribed in Example 1.

Example 1—Measurement of Residual Stress (Split-Ring Methods)

In general, when a pipe is cooled, the polymeric material closest to thebore of the pipe will cool slower than the outer surface of the pipe andconsequently there may be different levels of crystallinity across thethickness of the pipe wall—crystallinity may be highest towards thecentre of the pipe compared to the outer surface. Differences incrystallinity across a pipe wall set up different stresses in thepipe—the residual hoop stress is tensile on the pipe bore andcompressive on the outer surface. This effect can be used in assessingresidual stress in a pipe by cutting a ring from a pipe, forming a slitin it and assessing the split ring as it closes up in a controlled test.

Two methods are described below for assessing residual stress; the firstmethod is more appropriate for smaller diameter pipes (e.g. up to 20 mmdiameter) and the second method for larger diameter pipes (e.g. above 20mm diameter).

Method 1

Rings can be cut from the pipe and the wall thickness and originaldiameter (outside diameter) and average radius measured with appropriateinstruments. The pipe is then slit in the axial direction through aradius of the pipe. The slit closes in upon itself. The final diameteris then measured (average of at least two positions at 90° to eachother). The residual hoop stress may then be estimated from thefollowing equation:σ_(R) =Eh(ΔD)/(4πr ²)where E is the modulus of the pipe material, ΔD is the change in outsidediameter, r is the average radius and h is the wall thickness.

The following table summarises the results for a 6.3 mm internaldiameter PEEK pipe having a 1.22 mm wall thickness which was ‘crashcooled’ using water in a conventional sleeve calibrator and a pipe ofthe same dimensions which was fabricated using the novel apparatusdescribed herein.

Pipe Water Cooled Apparatus described (Prior art) herein (invention)Residual Stress (MPa) 6.7 2.4Method 2

Rings can be machined from a pipe and the widths, diameters and averagewall thicknesses measured. The rings are then slit axially as per Method1, and then pulled apart on a mechanical testing machine using a thinwire to apply the load (see the Hodgkinson paper referred tohereinafter). The load versus deformation trace shows an initial risefollowed by a clear change in gradient as the ring parted passes its‘un-slit’ position and begins to open out.

The maximum level of residual stress, σ_(R), in the pipes can bedetermined from the formulaσ_(R)=1.5P ₁(D−h)(1+1/π)/L h ²where P₁ is the load at which the trace changes gradient and the splitring parts, D is the external diameter, h is the wall thickness and L isthe length of the pipe sample

This assumes that residual stress is tensile on the pipe bore andcompressive on the outer surface, which is why the split rings close.

The following table summarises the results for a 5″ (Ω12.7 cm) diameterPEEK pipe which was ‘crash cooled’ using water in a conventional sleevecalibrator and an 8″ (Ω20.3 cm) diameter pipe which was fabricated usingthe apparatus described herein.

Pipe Size 5″ Pipe 8″ Pipe Residual Stress (MPa) 7.26 1.64

The residual stress calculated for the 5″ pipe (7.26 MPa) issignificantly higher than that calculated for the 8″ pipe (1.64 MPa).This can be seen in FIGS. 7(a) and (b) where greater closure (FIG. 7a )corresponds to higher residual stress.

The residual stress for the 5″ pipe is ˜7% of the yield stress, whereasthe residual stress for the 8″ pipe is ˜1.5% of the yield stress: theresidual stress in the 5″ pipe might be expected to have a significantinfluence on pipe performance.

Further detail on the test methods described can be found in “ResidualStresses in Plastics Pipes”, J. M. Hodgkinson and J. G. Williams,Deformation, Yield and Fracture of Polymers, Cambridge, 1982, thecontent of which is incorporated herein by reference.

The invention claimed is:
 1. A calibrator device for manufacturing apipe having a length of at least 1 m and a residual stress of less than5 MPa, said pipe comprising: a polymeric material which includes: (a)phenyl moieties; (b) ether and/or thioether moieties; and, optionally,(c) ketone and/or sulphone moieties, wherein the polymeric materialexhibits a crystallinity half-life (t_(0.5)) at 15° C. above its glasstransition temperature (Tg) of less than 1000 seconds; wherein thethickness of a wall which defines the pipe is in the range of 0.6 mm to6 mm or for use in a method comprising: (i) selecting a calibratordevice which includes an elongate opening for receiving a hot extrudedpipe, wherein said opening includes a vacuum applying region arranged toapply a vacuum to a pipe within the opening, said device furtherincluding at least two cooling regions which are spaced apart along itsextent, said cooling regions being arranged to cool a pipe within theopening; (ii) selecting the respective level of vacuum to be applied tosaid vacuum applying region; (iii) selecting the respective level ofcooling to be applied by said cooling regions; (iv) introducing a hotextruded pipe into said elongate opening in said calibrator andconveying said pipe through said elongate opening; (v) applying a vacuumto said pipe in said vacuum applying region; and cooling said pipe insaid cooling regions as the pipe is conveyed along said elongateopening, said calibrator device including an elongate opening forreceiving a hot extruded pipe, wherein said opening includes a vacuumapplying region arranged to apply a vacuum to a pipe within the opening,said device further including at least two cooling regions which arespaced apart along its extent, said cooling regions being arranged tocool a pipe within the opening, and each of said cooling regions havinga vacuum plate, wherein each vacuum plate is independentlytemperature-controlled with respect to the other vacuum plate.